The present invention relates to a water sparger for a boiling water reactor.
A conventional water sparger for a boiling water reactor is shown in FIGS. 1 and 2. A shroud 2 is disposed in a reactor pressure vessel 1, and a reactor core 3 is housed in the shroud 2. A mixture of steam and water which is generated in the reactor core 3 flows upward and is separated into steam and water in a steam separator 4. The steam is then separated from its moisture in a steam dryer 5 and is supplied from a main steam nozzle 6 to a turbine (not shown) through a main steam piping (not shown). The steam, after it has been used to drive the turbine, is condensed in a condenser (not shown) and returns to the reactor pressure vessel 1 through water spargers 7. The water separated from said mixture in the steam separator 4 is mixed with water sprayed from the water spargers 7. The mixed water flows downward through annular downcomers 8 formed between the inner face of the reactor pressure vessel 1 and the outer face of the shroud 2. The mixed water is then supplied to the lower portion of the reactor pressure vessel 1 by a plurality of reactor water circulators 9 which are circumferentially arranged below the downcomers 8. The mixed water flows from the bottom of reactor pressure vessel 1 into the core 3. The water flowing into the reactor core 3 is heated therein to become a mixture of steam and water. The mixture is then supplied to the steam separator 4 and is separated into water and steam. This water is mixed with water sprayed from the water spargers 7 and is supplied again to the lower portion of the reactor pressure vessel 1. The above-mentioned circulation is repeated. Each water sparger 7 has water supplying headers 10 each comprising an arcuate pipe, as shown in FIG. 2. The water supplying headers 10 are horizontally and circularly arranged so that water is sprayed from a number of nozzle orifices 11 formed on each water supplying header 10, whereby relatively hot water separated from the steam separator 4 is uniformly mixed with the relatively cool water sprayed from the water supplying headers 10.
The flow of the water separated in the steam separator 4 and the flow of the water sprayed from the water supplying headers 10 are schematically shown in FIG. 3. The hot water separated in the steam separator 4 spreads horizontally and radially and the flow downward in the downcomer 8 is substantially vertical. The hot water then flows into the reactor water circulators 9. The hot water with a flow rate Qa which flows in a region Wa flows into a reactor water circulator 9a; the hot water with a flow rate Qb which flows in a region Wb flows into a reactor water circulator 9b; and the hot water with a flow rate Qc which flows in a region Wc flows into a reactor water circulator 9c. Similarly, the water sprayed from the water supplying headers 10 with a flow rate qa in the region Wa is supplied to the reactor water circulator 9a; the water sprayed therefrom with a flow rate qb in the region Wb is supplied to the reactor water circulator 9b; and the water sprayed therefrom with a flow rate qc in the region Wc is supplied to the reactor water circulator 9c. The flow rates Qa, Qb and Qc are equal to each other. However, the flow rate distribution of the water sprayed from the water supplying headers 10 in the vicinity of the inner face of the reactor pressure vessel 1 can hardly be kept uniform due to a pressure drop in the water supplying headers 10 and other factors. As a result, the flow rates qa, qb and qc vary from each other. The total flow rates Qa and qa, Qb and qb, and Qc and qc differ from each other so that water discharged from the reactor water circulators 9 varies in temperature. For this reason, the temperature distribution of the water flowing into the reactor core 3 becomes nonuniform, leading to a nonuniform void fraction in the reactor core 3 preventing uniform reaction of the fuel and its complete combustion.
Hot water in the conventional steam separator 4 directly flows on the water supplying headers 10, thereby causing significant thermal stress to occur in the water supplying headers 10. Further, since the water supplying headers 10 are horizontally disposed, they interfere with an underwater TV camera and tools when such equipment is lowered in the downcomer for inspection of the reactor water circulators.